Six reasons to love your hot-shoe flash
3. Less redeye Because hot-shoe flashes are raised high above the lens axis, they eliminate (or greatly reduce) the possibility of redeye in people pictures.
4. More lens choices Built-in flashes and large lenses don't mix well. The popular 24-200mm and 35- 300mm superzooms, for example, are typically so large in length and girth that they block the output of built-in flash units, creating a dark semicircle at the bottom of every horizontal and on the side of every vertical picture, often regardless of subject distance or focal length. Because a hot-shoe flash usually sits high above the lens, your optical options grow exponentially.
5. Accessories A small industry is dedicated to producing accessories for shoe-mount flashes. Diffusers soften output for more attractive lighting; spreaders expand a hot-shoe's output to eliminate or reduce light falloff; bounce cards provide fill for shadows and spectral highlights for the eyes in bounce-lit portraits; and colored filters offer the possibility of balancing light sources of mismatched color temperatures.
6. Increased exposure options Shoe-mount flashes offer exposure options built-ins can't (or can, but usually don't): High-speed syncing, second curtain syncing, and manual output, for example. The most important of these expanded options is the ability to move the flash off the camera-either with an accessory TTL cable or even in a non-TTL manual mode-to light a background or a subject from behind or from the side. Try that with a built-in flash!
In fact, your hot-shoe flash doesn't even have to be TTL-dedicated (that is, controlled by through-the-lens metering). With today's digital SLRs, the exposure hassles that once complicated non-TTL flash operation are greatly minimized. Your DLSR's monitor tells you instantly if you need more or less light. And what the LCD image doesn't tell you about exposure, a histogram usually will.
The moral? If you've been sitting on the fence about adding a hot-shoe flash, jump.